1. Field
The present invention relates generally to communication, and more specifically to techniques for generating quality indicator bits (QIBs) in wireless communication systems.
2. Background
In a wireless (e.g., cellular) communication system, a user with a wireless terminal (e.g., a cellular phone) communicates with another user or entity via transmissions on the forward and reverse links with one or more base stations. The forward link refers to transmission from the base station to the terminal, and the reverse link refers to transmission from the terminal to the base station. The forward and reverse links are typically allocated different frequencies.
In a Code Division Multiple Access (CDMA) system, within the limit of physical channel resources, the total capacity of the forward link for each base station is determined by its total transmit power. Each base station may transmit data to a number of users concurrently on the same frequency band. A portion of the base station's total transmit power is then allocated to each active user such that the aggregate power allocated to all users is less than or equal to the total transmit power.
To maximize the forward link capacity, the amount of transmit power used for each terminal can be adjusted by a power control mechanism that attempts to achieve the desired level of performance with the minimum amount of transmit power. For a CDMA system, this power control mechanism is typically implemented with two power control loops. The first loop adjusts the transmit power such that the quality of the signal received at the terminal is maintained at a particular threshold level. The received signal quality is typically quantified by an energy-per-bit-to-noise-plus-interference ratio (Eb/Io). The threshold level is often referred to as the power control setpoint (or simply, the setpoint). The second loop adjusts the setpoint such that the desired level of performance is maintained. This level of performance is typically given by a particular frame error rate (FER), e.g., 1% FER. The forward link power control mechanism thus attempts to reduce power consumption and interference while maintaining the desired level of performance for the terminal. This then maximizes the forward link capacity.
Some CDMA systems support the feedback of several types of power control commands to control the base station's transmit power for a given terminal. For example, in a cdma2000 system, a terminal may send back power control bits, erasure indicator bits (EIBs), or quality indicator bits (QIBs) for power control purposes. A power control bit is typically generated by comparing the received signal quality for a particular transmission (e.g., data, pilot, and so on) against the setpoint. Each power control bit would then request the base station to adjust its transmit power for the terminal either up or down by a particular amount (e.g., 1 dB). An erasure indicator bit indicates whether a data frame transmitted earlier by the base station was received correctly or in error by the terminal. A quality indicator bit indicates whether a previous data frame transmitted by the base station was received with sufficient or insufficient signal quality. Depending on the particular power control mode selected for use, the terminal is then configured to periodically send one of these three types of power control command back to the base station.
If the terminal is configured to send back quality indicator bits, then each quality indicator bit is typically generated based on a data frame transmitted on a designated forward channel. However, this forward channel may be operated in a non-continuous manner whereby data frames may not be transmitted on the forward channel some of the times. This non-continuous transmission is also referred to as discontinuous transmission (DTX). DTX frames (i.e., null or empty frames) are not transmitted on the forward channel, and a DTX event indicates the lack of transmission in a given frame interval. When DTX events are detected, the normal method for generating quality indicator bits based on the received data frames cannot be used since none were transmitted.
In one simple method for dealing with non-continuous transmission on the forward channel, all frames determined as DTX events are classified as having good received signal quality. However, quality indicator bits generated in this manner would not provide useful information for power control purposes. The transmit power for the terminal cannot be properly adjusted based on these quality indicator bits.
There is therefore a need in the art for techniques to generate quality indicator bits for a non-continuous transmission on a forward channel in a wireless communication system.